Magnetic delayed arming device for fuses and boosters



S SOBELMAN Feb. 25, 1958 MAGNETIC DELAYED ARMING DEVICE FOR FUSES ANDBOOSTERS Filed 001:. 21, 1952 2 Sheets-Sheet l INVENTOR. EIidnEyEmbelmnn States MAGNETIC DELAYED ARMING DEVICE FOR FUSES AND BOOSTERSSidney Sobelman, Morris Plains, N. J., assignor to the United States ofAmerica as represented by the Secretary of the Army The inventiondescribed herein may be manufactured and used by or for the Governmentfor governmental purposes without the payment to me of any royaltythereon.

The present invention relates to a delay arming device forspin-stabilized projectiles.

The use of delay arming devices in fuses and boosters to maintain theexplosive train in a projectile in unarmed condition until theprojectile is free of the weapon and has traversed to a safe distance,is well known in the art. Such devices may involve mechanism which isarmed by means responsive to rotation of a projectile, as for examplearming blocks movable into position by centrifugally responsive geartrains, or ball rotors responsive to centrifugal force of a spinningprojectile to precess or rotate into armed position.

In projectiles employing a point detonating fuse, an explosive train isprovided which usually comprises a detonator of an extremely sensitivesubstance adapted to function instantaneously when struck by a firingpin upon impact or when flash initiated, and an explosive charge of aninsensitive nature which is set off by the detonator. If the fusecontains a booster, the detonator first sets off the booster chargewhich again is insensitive, and the booster in turn detonates theexplosive projectile charge.

In any case the sensitive detonator must be protected against prematuredetonation in the event an obstruction is encountered either in the boreof the weapon, or in flight in the vicinity of friendly personnelimmediately after the projectile emerges from the weapon. If prematuredetonation of the sensitive substance does occur in the bore of theweapon or before the projectile is clear of friendly personnel, a delayin movement of the detonator to completely armed position is desirablesince it will confine the explosion to the detonator alone and willprevent the flash from being communicated to the explosive charge.

It is accordingly an object of this invention to provide a delay armingdevice for a fuse or booster which is both bore safe and detonator safe.

It is also an object of this invention to provide a delay arming devicefor a fuse or booster constructed and arranged to maintain a break inthe continuity of the explosive train until the projectile has traveledto a safe location.

It is also a further object of this invention to provide a delay armingdevice for a rotating projectile fuse or booster including an armingball rotor movable from safe to armed position in response tocentrifugal force of the rotating projectile.

Still another object of this invention is to provide a delay armingdevice for a spin-stabilized projectile including an arming ball rotorwhich is held in safe position by the force of attraction betweenmagnets located in the body of the fuse and in the rotor, untilcessation of set back, whereupon the rotor is precessed to armedposition by the centrifugal force of the rotating projectile.

With these and other objects in view which will become apparent as thefollowing specification develops,

atent ice reference is made to the accompanying drawing forming a partof the specification wherein like numerals are used to designatecorresponding or similar parts in the several views and wherein:

Figure 1 is a transverse sectional view of the magnetically restrainedrotor of my invention as applied to a booster.

Figure 2 is a section taken on line 2"-2 of Figure 1.

Figure 3 is an isometric view of the body magnets, rotor magnet andkeeper.

Figures 4 and 5 represent a modification of the are rangeme'nt in Figure1 with the rotor magnet eliminated and with a section of the rotormagnetized instead.

Figures 6, 7 and 8 illustrate another modification using a cylindermagnet as a liner for the detonator.

Referring to Figures 1, 2 and 3 wherein the same numerals are used todesignate the same parts in the several views reference character 1designates a booster assembly for a projectile fuse comprising a maincylindrical body portion 2 extennally threaded at 3 to screw threadedlyreceive the correspondingy threaded portion of a fuse (not shown). Theupper portion of body 2 is provided with a cylindrical bore 4 ofsubstantial diameter having a depth about one third the depth of thebody, leading into a counterbore 5 of reduced diameter and ofapproximately the same depth as bore 4. Counterbore 5 is internallythreaded at 6 to screw threadedly receive a cylindrical insert 7 havinga lesser depth than coun'terbore 5 and so disposed within thecounterbore to provide a narrow cylindrical space 8 between the lowerend of insert 7 and the bottom of counterbore 5. Insert 7 is providedcentrally with a downwardly opening spheroidal cavity whichall'ochirally mates with a shallower upw'ardly opening axial cavity inthe lower third of body portion 2, to form a spherical cavity 9 forreceiving an arming ball rotor 10 of a diamagnetic substance such brassor any of the well-known plastics. The ball rotor is provided with adiametral bore 11 terminating in a reduced axial bore 12 which forms anannular shoulder 13 to support the lower end of a detonator capsule 14,tightly received in bore 11.

The magnetic system for restraining rotation of the arming ball rotorcomprises a bar rotor magnet 15 snugly fitted into an off-center bore 16formed transversely in the ball rotor just below the lower side wall ofdetonator capsule 14 when restrained in safe position as seen inFigure 1. The rotor magnet is provided with a keying slot or cavity 17midway between the ends thereof, and in its top surface, to receive therounded surface of the detonator capsule wall to thereby retain themagnet in place within the rotor (see Fig. 3). The opposed ends of therotor magnet are curved as at 18 and 18a to conform with the contour ofthe ball rotor. The body 3 of the booster assembly is provided withhorizontal recesses 19, 19a directly below the bottom wall ofcounterbore 5 and extending transversely on opposed sides of rotor mag Inet 15, to receive bar magnets 20, 20a, with inner'en'ds 21, 21a curvedto conform with the curved ends of the rotor magnet when the ball rotoris in unarmed position. The magnets may be made of a compositionconsisting of aluminum, nickel and cobalt, commonly known as Alnico, ora similar substance having paramagnetic properties. To complete themagnetic circuit, a toroidal keeper 22 of soft iron, or the like isreceived in space 8 to encompass ball rotor 10 and with its. bottom wallabuttingthe top surface of magnets 20, 2011. Keeper 22 acts to preservethe intensity of magnetization in the well-known manner.

A cup shaped member 23 is screwed to the lower half of threads 3 on body2 with its bottom axially spaced from the lower end of body 2 to provideachamber 24 inwhich is received an explosive booster ehar e zs.

An axial passage 26 is formed in body 2 to extend between the sphericalcavity 9 and chamber 24 such that when the ball rotor is moved inclockwise direction to armed position, passage 26 and bores 11 and 12are in axial alinement to provide a continuous flash passage between thedetonator and booster. Alternatively a leadin explosive capsule 27 ofless sensitivity than the booster chargemay be interposed in passage 26if desired. Also, insert 7 is provided with an axial fiash'passage 28 topermit passage therethrough either of a firing pin or flash in thewell-known manner.

Theoperation of the device is obvious from the above description. As canreadily be seen, the north and south poles ofthe magnets are relativelydisposed so as to achieve maximum magnetic attraction when the ballrotor is in unarmed or safe position. This attraction restrains therotor magnet and the rotor from movement especially in view of theofi-center location of the'rotor magnet in the rotor assembly. Althoughnormal handling in shipment and in the field, or in the event the fuseor projectile is dropped, may cause the rotor to move with respect tothe fuse body, the force of the magnetic field will immediately swingthe rotor assembly back to safe position. Additionally if theextremely'sensitive detonator is inadvertently set off, the break incontinuity of vthe flash passage resulting from the force of attractionof the magnets will preclude detonation of the lead in and boostercharges.

. When a projectile containing the fuse of my invention is fired from aweapon, set back forces will increase frictional resistance between theball rotor and the abutting surfaces of the spherical cavity, and theseforces together with the magnetic force of attraction are sufficient. tooverride the effects of centrifugal force-to prevent precession of theball rotor until the projectile is free ofthe weapon. Upon cessation ofset back, when the projectile is free of the weapon, centrifugal forcewill now .be sufiicient to overcome the effects of the magneticattraction to cause the ball rotor to precess to armed position.

Obviously the parts may be designed for suflicient time to elapsebefore'the fuse is fully armed, to enable the projectile to traverse toa safe distance so that if obstruction is encountered to detonate thefuse, friendly personnel will not be endangered by premature explosion.

It is to be understood that proper adjustment must be made due to theshift in center of gravity of the ball rotor caused by the differencesin specific gravity between the brass-rotor and the fAlnico rotormagnet. Additionally, notwithstanding the decrease in effectiveness ofthe magnetic field, as the rotormagnet moves farther away from the bodymagnets, a certain amount of magnetic attraction will remain which mayprevent the ball rotor from moving to fully armed position. To obviatethis tendency a compensating hole 29 may be drilled in the ball rotor.The location of this hole must be such as to angularly shift the axis ofthe maximum moment of inertia in a counterclockwise direction, as theparts are viewed in Figure 1. As this axis tends to aline with the axisof spin of the projectile, the rotor, when rotating at average speedwill tend 'to over shoot the fully armed position. By making the hole ofproper size, depth and location, the magnetic couple tending to hold therotor from the fully armed position is overcome or nullified.

Referring to the modification in Figures 4 and the booster assembly isdesignated as reference character 1', and is provided with cylindricalbody portion 2' externally threaded at 3' and having upper cylindricalbore 4', and counterbore 5. counterbore 5 is provided with threads 6 forreceiving insert 7'. Arming ball rotor which in this modification is ofmagnetizable metal, is

received in spherical cavity 9' formed partly in insert 7' and partly inbody 2, and the rotor 10' is provided with diametral bore 11'. receivedin bore 11'. However in place of a rotor mag. net 15 an off-centertransverse section of the ball rotor;-

Detonator capsule 14 is snugly.

15 directly below the side wall of capsule 14 is magnetized. Similarlyas in the species of Figure 1 recesses 19' and 19a are provided in body2' to receive magnets 20' and 20a curved as at 21 and 21a to conformwith the ball rotor 10. A keeper- 22' is received in a space 8' formedbetween insert 7' and the bottom of counterbore 5', and in like'manner abooster cup 23' is screwed onto body 2, to form chamber 24' forreceiving a booster charge 25. An axial passage 26' to receive a lead-in27 is formed in body 2' between chamber 24 and spherical cavity 9, andinsert 7' is also provided with an axial passage 28' to permitinitiation. of thedetonator.

If need be a compensating hole (not shown) may also be drilled in rotor10' to compensate for the tendency of the remaining magnetic attractionbetween the magnetized rotor and magnets 20', 20a, which would otherwiseprevent full arming of the ball rotor. The operation of this system isexactly the same as the species illustrated by Figures 1 and 2, hence itwill not be de-' scribed.

Figures 6, 7 and 8 delineate yet another modification wherein a cylindermagnet forming a part of the magnetic restraint system, is also used asa liner for the detonator body portion 102 is provided with acylindrical bore 104 of substantial diameter leading into a counterbore105 of slightly reduced diameterbut having a depth substantially equalto the depth of bore 104. The side wall of counterbore 105 isscrew-threaded at 106 to receive an externally threaded plug or insert107 approximately one half the depth of counterbore 105, and so disposedin the'counterbore to forma cylindrical space 108 between the lowersurface of plug 107 and the bottom of counterbore 105., Plug 107, andthe section of body portion 102 beneath the lower extremity ofcounterbore are provided respectively withv axially opposed,allochirally mated spherical cavities '109 and 110 adapted to receivebetween them for rotation only an arming ball rotor 111 which may bemade of brass or some other diamagnetic substance such as anyof the wellknown plastics.

' Rotor 111 is provided with a diametral bore 112 of substantialdiameter 'lined with a cylindrical magnetic sleeve or insert 113 ofAlnico, or the like crimped into place in the rotor as at 114, 115.Within the bore of sleeve 113there is received a detonator capsule 116having one side abutting a shoulder 117 formed in the sleeve, and theopposed side engaged by a split-ring detonator retainer 118 adapted tohold the capsule in place within the liner. A toroidal keeper 119concentric about rotor 111 and with its axial bore 119' of greaterdiameter than ball rotor 111 is tightly received in space 108, and in"the lower half of its wall on one side, the keeper is provided with arecess 120 in longitudinal alineme'nt with a mating recess 121 in body102 for receiving a bar magnet 122, extending into bore 119 and curvedas at 123 to conform to the contour of ball rotor 111. On the sideopposed to recess 120, the wall of keeper 119 is slotted as at 124 toreceive a magnet 124a which engages the side wall of counterbore 105 atits outer extremity, the inner end extending into bore 119 and curved asat 125 to conform with the contour of arming ball rotor 111.

The rest of the booster assembly 101 is similar in design to the speciesillustrated in Figures '1 and 2 and in like manner comprises booster cup126, booster chamber 127, booster charge 128, axial flash passage 129 toreceive alead-in 130 and compensating'hole 131. In sert 107 is alsoprovided with a frusto-conical axial passage 132 which will communicatewith the axial bore in the ball rotor when the rotor is infully armedposition. As the magnets are" not duplicates, no error can arise inassembly. The magnetic field of flux is axially past the detonator andcircumferentially through the keeper.

Obviously the description of operation for this modification is similarto the operation for the first species and need not be described.

While my invention has been illustrated as being applicable to a boosterassembly for the type of fuse commonly associated with a spin-stabilizedprojectile, it is to be understoodthat other adaptations within thepurview and scope of this specification are also possible. For examplethe magnetic restraining system may also be utilized in aerial dropbombs having fins to cause the bomb to spin in descent. Numerous othermodifications and alterations of the structures disclosed andillustrated will be apparent to one skilled in the art, and it isobvious that such modifications may be made without departing from thespirit of the invention as defined in the following claims.

What I claim is:

1. In a point detonating fuse for a rotating projectile, a main bodyportion having a spherical cavity and an axial flash passagewayforwardly of said cavity, a spheroidal rotor in said cavity having adiametral bore with its axis lying crosswise of the axis of said flashpassage when said fuse is unarmed, a detonator in said diametral bore,first magnetic means in said rotor, and second magnetic means in saidbody interacting with said first magnetic means to normally urge saidrotor into unarmed position; upon firing said projectile to precess saidrotor to armed position, said magnets retarding precession of said rotorto delay arming of said fuse.

2. In a point detonating centrifugally armed fuse, a body having anaxial flash passage therein, a ball rotor mounted for universal rotationin said body rearwardly of said flash passage, said rotor having adiametral bore lying crosswise of the axis of said flash passage whensaid fuse is unarmed and determining an axis of maximum moment ofinertia, and magnetic means in said body interacting with magnetic meansin said rotor to hold said rotor in unarmed position; upon firing theprojectile supporting said fuse said magnetic means continuing tointeract to retard precession of said rotor to armed position.

3. In a point detonating centrifugally armed fuse for a spin-stabilizedprojectile having a longitudinal axis, a booster assembly comprising abody received in said fuse, said body having a spherical cavity formedtherein, a centrifugal ball rotor rotatable in said cavity from firstsafe position to second armed position, said ball rotor having adiametral bore lying crosswise of said longitudinal axis when said rotoris in safe position, said body having an axial passage forwardly of saidball rotor in axial alinement with said diametral bore when said rotoris in armed position, a detonator in said diametral bore, andinteracting magnetic means on said body and said rotor urging said rotorinto said crosswise position, said ball rotor is made of a diamagneticsubstance, and said magnetic means comprises a rotor magnet received ina hole formed transversely in said rotor subjacent said detonator,interacting with a pair of magnets each lying in recesses formed in saidbody on opposed sides of said rotor magnet in horizontal alinementtherewith.

4. In a point detonating centrifugally armed fuse for a spin-stabilizedprojectile having a longitudinal axis, a booster assembly comprising abody adapted to be received in said fuse, said body having a sphericalcavity formed centrally therein, a centrifugal diamagnetic ball rotorrotatable in said cavity from first safe position to second armedposition, said ball rotor having a diametral bore lying crosswise ofsaid longitudinal axis when said rotor is in safe position, said bodyhaving an axial passageway forwardly of said ball rotor in axialalinement with said diametral bore when said rotor is in 6 armedposition, a paramagnetic sleeve liner snugly fitting said diametralbore, a detonator in the bore of said sleeve liner, and a pair ofmagnets in said body in recesses on opposed sides of said rotorinteracting with said sleeve magnet to urge said rotor into cross-wiseposition.

5. A fuse for a spin stabilized projectile comprising a fuse body, acentrifugally responsive arming rotor within said fuse body adapted toprecess from safe to armed pdsition upon firing of said projectile, arotor magnet, a pair of body magnets normally axially aligned with eachpole of said rotor magnet and spaced therefrom, said magnets norm-allyholding said rotor in safe position; upon firing said projectile toprecess said rotor to armed position, said magnets retarding precessionof said rotor to delay arming of said fuse.

6. A point detonating centrifugally armed fuse for a spin stabilizedprojectile having a longitudinal axis comprising a body in said fusehaving an axial passageway, 21 ball rotor mounted for universal rotationin said body rearwardly of said passageway, said rotor having adiametral bore lying crosswise of said longitudinal axis when said fuseis unarmed and determining an axis of maximum moment of inertia,magnetic means in said body interacting with magnetic means in saidrotor to prevent coincidence of said diametral bore with saidlongitudinal axis during handling and retard precession of said rotor toarmed position in response to centrifugal force of a spin stabilizedprojectile, said ball rotor is made of a diamagnetic substance, and saidmagnetic means comprises a rotor magnet received in a hole formedtransversely in said rotor subjacent said detonator, interacting with apair of magnets each lying in recesses formed in said body on opposedsides of said rotor magnet in horizontal alinement therewith.

7. A delay arming, point detonating fuse for a spin stabilizedprojectile comprising, a main body portion having a spherical cavitytherein, an aiming ball rotor mounted for universal rotation within saidcavity, a first bore through said rotor, a detonator in said first bore,a second bore through said rotor, a rotor magnet within said secondbore, a pair of body magnets on each side of said rotor in spacedalignment with said rotor magnet, means to preserve the intensity ofsaid body magnets, said body magnets interacting with said rotor magnetto normally hold said rotor in unarmed position; upon firing saidprojectile, said rotor precessing to armed position against theretarding action of said magnets.

8. A delay arming, point detonating fuse for a spin stabilizedprojectile comprising, a main body portion having a spherical cavitytherein, an arming ball rotor mounted only for universal rotationalmovement within said cavity, a detonator within said rotor, a rotormagnet within said rotor, a pair of body magnets on each side of saidrotor in spaced alignment with said rotor magnet, means to preserve theintensity of said body magnets, the intensity of magnetization of saidmagnets and the spacing ther'ebetween being suificient to overcomerotation of said rotor during normal handling of said fuse andprojectile; upon firing said projectile, said rotor precessing to armedposition against the retarding force of said magnets whereby the armingtime of said fuse is prolonged.

References Cited in the file of this patent UNITED STATES PATENTS384,662 Zalinski June 19, 1888 1,197,729 Flather Sept. 12, 19161,428,203 Asbury Sept. 5, 1922 2,436,396 McCaslin Feb. 24, 19482,441,939 Nichols May 18, 1948 2,455,620 Sreb Dec. 7, 1948 2,626,568Podnos et a1 Jan. 27, 1953

